U.S. patent number 7,328,019 [Application Number 11/197,471] was granted by the patent office on 2008-02-05 for communication environment measurement method for mobile station and the mobile station.
This patent grant is currently assigned to Fujitsu Limited. Invention is credited to Takurou Nishikawa, Masaaki Suzuki.
United States Patent |
7,328,019 |
Nishikawa , et al. |
February 5, 2008 |
Communication environment measurement method for mobile station and
the mobile station
Abstract
In a communication system for respectively transmitting pilot
signals from a plurality of base stations to a mobile station via a
first channel and also for transmitting data from one base station
to a mobile station via a second channel, the mobile station
corrects total receive power at the time of handover by subtracting
power of the data signal received via the second channel from the
total receive power of the signals received from a base station in
communication (serving cells) via the second channel, then corrects
the total noise power based on the total receive power after the
correction, and measures the communication environment between the
base station and the mobile station using the power of the pilot
signal received from the base station in-communication and the
corrected total noise power.
Inventors: |
Nishikawa; Takurou (Kawasaki,
JP), Suzuki; Masaaki (Kawasaki, JP) |
Assignee: |
Fujitsu Limited (Kawasaki,
JP)
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Family
ID: |
36569761 |
Appl.
No.: |
11/197,471 |
Filed: |
August 5, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060211391 A1 |
Sep 21, 2006 |
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Foreign Application Priority Data
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Mar 17, 2005 [JP] |
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2005-076651 |
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Current U.S.
Class: |
455/436; 455/68;
455/453; 455/452.2; 455/226.1; 455/226.3; 455/69 |
Current CPC
Class: |
H04W
36/0085 (20180801); H04W 36/12 (20130101); H04W
36/30 (20130101) |
Current International
Class: |
H04B
17/00 (20060101) |
Field of
Search: |
;455/436,452.2,453,68,69,226.1,226.3 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO 93/12623 |
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Jun 1993 |
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WO |
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WO 02/089502 |
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Nov 2002 |
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WO |
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Other References
3GPP TS 25.212, Jun. 2004. cited by other .
3GPP TS 25.214, Jun. 2004. cited by other.
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Primary Examiner: Feild; Joseph
Assistant Examiner: Smith; S.
Attorney, Agent or Firm: Bingham McCutchen LLP
Claims
What is claimed is:
1. A communication environment measurement method in a mobile
station included in a communication system which respectively
transmits pilot signals from a plurality of base stations to a
mobile station and controls a hard handover by switching a channel
for data transmission to said mobile station based on the
communication environment between each base station and the mobile
station, including steps of: measuring the communication
environment between a source base station of said channel and said
mobile station, and the communication environment between another
base station and said mobile station for said handover control, and
compensating relative deterioration of the measurement result of
the communication environment on the source base station of said
channel in comparison with the measurement result of the
communication environment on said other base station, the relative
deterioration being caused by the transmission of said channel,
wherein said step of compensating includes: measuring total receive
power of the signals received from the source base station of said
channel; measuring power of the signal of said channel received
from the source base station of said channel; measuring signal
power of the pilot signal received from the source base station of
said channel; correcting the total receive power by subtracting the
power of the signal via said channel from said total receive power;
calculating total noise power based on the total receive power
after said correction, and measuring the communication environment
between the source base station of said channel and said mobile
station using said pilot power and said total noise power.
2. The communication environment measurement method according to
claim 1, said step of calculating the total noise power includes:
storing ratio of the total receive power and internal noise power
generated inside a mobile station in association with a value of
each total receive power in the form of a table in advance;
calculating the internal noise power according to the total receive
power after said correction using said association table, and
calculating said total noise power by adding said internal noise
power to external noise power.
3. A communication environment measurement method in a mobile
station included in a communication system which respectively
transmits pilot signals from a plurality of base stations to a
mobile station and controls a hard handover by switching a channel
for data transmission to said mobile station based on the
communication environment between each base station and the mobile
station, including steps of: measuring the communication
environment between a source base station of said channel and said
mobile station, and the communication environment between another
base station and said mobile station for said handover control, and
compensating relative deterioration of the measurement result of
the communication environment on the source base station of said
channel in comparison with the measurement result of the
communication environment on said other base station, the relative
deterioration being caused by the transmission of said channel,
wherein said step of compensating includes: measuring total receive
power of the signals received from said other base station;
measuring signal power of the pilot signal received from said other
base station; estimating signal power in a case where a signal is
received from said other base station via said channel; correcting
the total receive power by adding said estimated signal power to
the total receive power of the signals received from said other
base station; calculating total noise power based on the total
receive power after said correction; and measuring the
communication environment between said other base station and said
mobile station using the signal power of the pilot signal received
from said other base station and said total noise power.
4. The communication environment measurement method according to
claim 3, wherein said step of estimating includes; measuring the
power of the pilot signal received from said source base station;
measuring the power of the signals of said channel received from
said source base station; and computing ratio of the power of the
pilot signal received from said source base station and the signal
power of the signal received via said channel from the source base
station; and estimating said power of the signal received via said
channel from said other base station using the power of said pilot
signal received from said other base station and said ratio.
5. The communication environment measurement method according to
claim 3, wherein said step of calculating the total noise power
includes: storing ratio of the total receive power and internal
noise power generated inside a mobile station in association with a
value of each total receive power in the form of a table in
advance; calculating the internal noise power according to the
total receive power after said correction using said association
table, and calculating said total noise power by adding said
internal noise power to external noise power.
6. A mobile station included in a communication system which
respectively transmits the pilot signals from a plurality of base
stations to a mobile station and controls a hard handover by
switching a channel for data transmission to said mobile station
based on the communication environment between each base station
and the mobile station, comprising: a measuring unit for measuring
communication environment between a source base station of said
channel and said mobile station and the communication environment
between another base station and said mobile station for said
handover control, and a compensation unit for compensating relative
deterioration of the measurement result of the communication
environment on the source base station of said channel in
comparison with the measurement result of the communication
environment on said other base station, the relative deterioration
being caused by the transmission of said channel, wherein said
compensation unit comprises: a total receive power measurement unit
for measuring total receive power of the signals received from the
source base station of said channel; a signal power measurement
unit for measuring power of the signal of said channel received
from the source base station of said channel; a pilot signal power
measurement unit for measuring signal power of the pilot signal
received from the source base station of said channel; and a
communication environment measurement unit for correcting the total
receive power by subtracting the power of the signal via said
channel from said total receive power, calculating total noise
power based on the total receive power after said correction, and
measuring the communication environment between the source base
station of said channel and said mobile station using said pilot
signal power and said total noise power.
7. The mobile station according to claim 6, further comprising a
storage unit for storing ratio of the total receive power and
internal noise power generated inside a mobile station in
association with a value of each total receive power in the form of
a table in advance, wherein said communication environment
measurement unit calculates the internal noise power according to
the total receive power after said correction using said
association table, and calculates said total noise power by adding
said internal noise power to external noise power.
8. The mobile station according to claim 6, further comprising a
communication environment measurement unit for measuring the
communication environment between said other base station and said
mobile station using a pilot signal received from said other base
station.
9. The mobile station according to claim 6, including: means for
determining maximum SIR, which is a ratio of the pilot signal power
and the noise signal power, out of the SIRs of a plurality of base
stations measured when the communication environment between said
base station and the mobile station was measured as SIR, and
feeding back the communication environment instruction value
corresponding to said maximum SIR to said source base station.
10. A mobile station included in a communication system which
respectively transmits the pilot signals from a plurality of base
stations to a mobile station and controls a hard handover by
switching a channel for data transmission to said mobile station
based on the communication environment between each base station
and the mobile station, comprising: a measuring unit for measuring
communication environment between a source base station of said
channel and said mobile station and the communication environment
between another base station and said mobile station for said
handover control, and a compensation unit for compensating relative
deterioration of the measurement result of the communication
environment on the source base station of said channel in
comparison with the measurement result of the communication
environment on said other base station, the relative deterioration
being caused by the transmission of said channel, wherein said
compensation unit includes: a total receive power measurement unit
for measuring total receive power of the signals received from said
other base station; a pilot signal power measurement unit for
measuring signal power of the pilot signal received from said other
base station; and a communication environment measurement unit for
estimating signal power in a case where a signal is received from
said other base station via said channel, correcting the total
receive power by adding said estimated signal power to the total
receive power of the signals received from said other base station,
calculating total noise power based on the total receive power
after said correction, and measuring the communication environment
between said other station and said mobile station using the signal
power of the pilot signal received from said other base station and
said total noise power.
11. The mobile station according to claim 10, wherein said
communication environment measurement unit comprises: a pilot
signal power measurement unit for measuring the power of the pilot
signal received from said source base station; a signal power
measurement unit for measuring the power of the signals of said
channel received from said source base station; and an estimation
unit for computing ratio of the power of the pilot signal received
from said source base station and the signal power of the signal
received via said channel from the source base station, and
estimating said power of the signal received via said channel from
said other base station using the power of said pilot signal
received from said other base station and said ratio.
12. The mobile station according to claim 10, wherein said
communication environment measurement unit includes: a storage unit
for storing ratio of the total receive power and internal noise
power generated inside a mobile station in association with a value
of each total receive power in the form of a table in advance; and
a noise power correction unit for calculating the internal noise
power according to the total receive power after said correction
using said association table, and correcting said total noise power
by adding said internal noise power to external noise power.
13. A mobile station included in a communication system which
respectively transmits the pilot signals from a plurality of base
stations to a mobile station and controls a hard handover by
switching a channel for data transmission to said mobile station
based on the communication environment between each base station
and the mobile station, comprising: a judgment unit for judging the
timing when data is not communicated via said channel referring to
the control channel to be transmitted from the source base station
of said channel; a communication environment measurement unit for
measuring the communication environment between the source base
station of said channel and said mobile station based on the pilot
signal received from the source base station of said channel at
said timing, a communication environment measurement unit for
measuring the communication environment between said other base
station and the mobile station based on a pilot signal received
from said other base station which is not in-communication; and a
communication environment reporting unit for reporting said
measured communication environments to the source base station.
14. A communication environment measurement method in a mobile
station included in a communication system which respectively
transmits pilot signals from a plurality of base stations to a
mobile station and controls a hard handover by switching a channel
for data transmission to said mobile station based on the
communication environment between each base station and the mobile
station, including steps of: measuring the communication
environment between a source base station of said channel and said
mobile station, and the communication environment between another
base station and said mobile station for said handover control;
compensating relative deterioration of the measurement result of
the communication environment on the source base station of said
channel in comparison with the measurement result of the
communication environment on said other base station, the relative
deterioration being caused by the transmission of said channel; and
adjusting compensating quantity at the timing of compensating based
upon the measurement result of reception quality of said channel
sent from the source base station.
15. A mobile station included in a communication system which
respectively transmits the pilot signals from a plurality of base
stations to a mobile station and controls a hard handover by
switching a channel for data transmission to said mobile station
based on the communication environment between each base station
and the mobile station, comprising: a measuring unit for measuring
communication environment between a source base station of said
channel and said mobile station and the communication environment
between another base station and said mobile station for said
handover control; a compensation unit for compensating relative
deterioration of the measurement result of the communication
environment on the source base station of said channel in
comparison with the measurement result of the communication
environment on said other base station, the relative deterioration
being caused by the transmission of said channel; and an adjustment
unit for adjusting compensating quantity at the timing of
compensating based upon the measurement result of reception quality
of said channel sent from the source base station.
16. The mobile station according to claim 15, wherein the
compensation unit executes compensation by upward-correcting said
measurement result of the communication environment on the source
base station of said channel or downward-correcting said
measurement result of the communication environment on said other
base station.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a communication environment
measurement method for a mobile station and a mobile station, and
more particularly to a communication environment measurement method
for a mobile station in a communication system where data is
transmitted from one base station to the mobile station, and the
mobile station.
A W-CDMA (UMTS) mobile communication system is a radio
communication system where a line is shared by a plurality of
users, and comprises a core network 1, radio base station
controllers (RNC: Radio Network Controller) 2 and 3,
multiplexers/demultiplexers 4 and 5, radio base stations (Node B)
6.sub.1-6.sub.5 and mobile station (UE: User Equipment) 7, as FIG.
15 shows.
The core network 1 is a network for routing in the mobile
communication system, and the core network can be constructed by an
ATM switching network, a packet switching network or a router
network, for example. The core network 1 is also connected with a
public network (PSTN), so that the mobile station 7 can
communication with fixed telephones.
The radio base station controllers (RNC) 2 and 3 are positioned as
the host of the radio base stations 6.sub.1-6.sub.5, and have a
function to control these radio base stations 6.sub.1-6.sub.5 (e.g.
management of radio resources to be used). The radio base station
controllers 2 and 3 also have a handover control function, which is
a function for receiving signals sent by one mobile station 7 from
a plurality of radio base stations at hand over, selecting data
signal having the best quality, and sending it to the core network
1 side.
The multiplexers/demultiplexers 4 and 5 are installed between the
RNC and a radio base station, and perform control to demultiplex
the signals addressed to each radio base station received from the
RNCs 2 and 3, and outputs them to each radio station as well as to
multiplex signals from each radio station, and transfers them to
each RNC.
The radio resources of the radio base stations 6.sub.1-6.sub.3 are
managed by the RNC 2, and the radio resources of the radio base
stations 6.sub.4 and 6.sub.5 are managed by the RNC 3, to perform
radio communication with the mobile station 7. The mobile station
7, which exists in one of the radio areas of the radio base
stations 6.sub.1-6.sub.5, establishes the radio line with one of
the radio base stations 6.sub.1-6.sub.5, and communicates with
another communication device via the core network 1.
The interface between the core network 1 and the RNCs 2 and 3 is
called the Iu interface, the interface between the RNCs 2 and 3 is
called the Iur interface, and the interface between the RNCs 2 and
3 and each radio base station 6.sub.1-6.sub.5 is called the Iub
interface, the interface between the radio base stations
6.sub.1-6.sub.5 and the mobile station 7 is called the Uu
interface, and the network composed of devices 2-6 in particular is
called a radio access network (RAN). The lines between the core
network 1 and the RNCs 2 and 3 are shared by Iu and Iur interfaces,
and the lines between the RNCs 2 and 3 and the
multiplexers/demultiplexers 4 and 5 are shared by Iub interfaces
for a plurality of radio base stations.
The above is a description on a general mobile communication
system, but now a technology to allow high-speed downstream data
transmission, such as HSDPA (High-Speed Downlink Packet Access), is
becoming incorporated into mobile communication systems (see 3G TS
25.212 (3rd Generation Partnership Project: Technical Specification
Group Radio Access Network; Multiplexing and Channel Coding (FDD));
and 3G TS 25.214 (3rd Generation Partnership Project: Technical
Specification Group Radio Access Network; Physical Layer Procedure
(FDD)).
HSDPA
HSDPA is a method for switching the transmission rate according to
the radio environment between a radio base station and a mobile
station, and switches the data size per one transport block
depending on the radio environment, or adaptively switches the
encoding modulation method. In the case of adaptive modulation and
coding (AMC), the QPSK modulation scheme and the 16QAM scheme are
adaptively switched, for example.
The HSDPA uses H-ARQ (Hybrid Automatic Repeat reQuest). In H-ARQ,
if the mobile station detects an error in the receive data from the
radio base station, a retransmission request (NACK signal) is sent
to the radio base station. The radio base station that received
this retransmission request retransmits the data, so the mobile
station performs the error correction decoding using the already
received data and the retransmitted receive data. In this way, in
the case of H-ARQ, the already received data is effectively used
even if an error occurs, so the gain of the error correction
decoding increases and as a result the retransmission count can be
suppressed to be low. If an ACK signal is received from a mobile
station, data transmission is a success and retransmission is
unnecessary, so the next data is transmitted.
The main radio channels to be used for HSDPA are, as FIG. 16 shows,
(1) HS-SCCH (High Speed-Shared Control Channel), (2) HS-PDSCH (High
Speed-Physical Downlink Shared Channel), and (3) HS-DPCCH (High
Speed-Dedicated Physical Control Channel).
Both HS-SCCH and HS-PDSCH are shared channels in the downstream
direction (downlink from the radio base station to a mobile
station), and HS-SCCH is a control channel for transmitting various
parameters on the data to be transmitted via HS-PDSCH. In other
words, this is a channel for notifying that the data is transmitted
via HS-PDSCH. The various parameters include, for example, the
destination information of the mobile station to which the data is
transmitted, the transmission bit rate information, the modulation
scheme information on the modulation scheme with which data is
transmitted via the HS-PDSCH, the number of allocated spreading
codes (code count), and the pattern of the rate matching to be
performed on the transmission data.
The HS-DPCCH, on the other hand, is a dedicated control channel in
the upstream direction (uplink from a mobile station to a radio
base station), and is used to transmit the respective receive
result (ACK signal, NACK signal), depending on the presence of an
error in the data received via the HS-PDSCH, to the radio base
station. In other words, this is a channel to be used to transmit
the receive result of the data received via the HS-PDSCH. If the
mobile station fails in received data (e.g. receive data has a CRC
error), the NACK signal is transmitted from the mobile station, so
the radio base station executes retransmission control.
The HS-DPCCH is also used when the mobile station, which measures
the receive quality such as SIR of the signal received from the
radio base station, transmits this receive quality to the radio
base station as CQI (Channel Quality Indicator). In other words,
CQI is the information for the mobile station to report the receive
environment to the base station and, for example, CQI value is
1-30, where CQI value is determined so that the block error rate
BLER, does not exceed 0.1 and reported to the base station.
For example, the mobile station holds a CQI table, and determines a
CQI value corresponding to the receive quality (SIR) from this CQI
table, and transmits this value to the radio base station via the
HS-DPCCH.
The radio base station judges whether the radio environment in the
downstream direction is good or not by the received CQI, and if
good, the radio base station switches the modulation scheme to one
that can transmit data faster, and if not good, it switches the
modulation scheme to one that transmits data slower (that is
performs adaptive modulation). Actually the base station has a CQI
table which defines formats with different transmission speeds
according to CQI=1-30, and determines the parameters (e.g.
transmission speed, modulation method, multiplexed code count)
according to the CQI value obtained from this CQI table, and
notifies these parameters to the mobile station by HS-SCCH, and
also transmits the data to the mobile station by HS-PDSCH based on
these parameters.
Channel Structure
FIG. 17 is a diagram depicting the timing of the channels in the
HSDPA system. In W-CDMA, which uses code division multiple access,
the codes separate each channel. The CPICH (Common Pilot Channel)
and the SCH (Synchronization Channel) are shared channels in the
downstream direction. The CPICH is a channel used at a mobile
station for channel estimation and cell search, and is a channel
for transmitting the so called pilot signals. SCH is further
divided into P-SCH (Primary SCH) and S-SCH (Secondary SCH), and is
a channel which is transmitted in bursts by the first 256 chips of
each slot. This SCH is received by a mobile station which performs
three-level cell search, and is used for establishing slot
synchronization and frame synchronization and for identifying the
base station code (scramble code). SCH is 1/10 the length of one
slot, but is shown to be a little wider than this in FIG. 17. The
remaining 9/10 is P-CCPCH (Primary-Common Control Physical
Channel).
Now the timing relationship of the channel will be described. In
each channel, 15 slots constitute one frame (10 ms), and one frame
has a length equivalent to 2560 chip lengths. As described above,
CPICH is used as a reference for other channels, so the beginning
of the frame of the SCH and HS-SCCH match the beginning of the
frame of CPICH. The beginning of the frame of the HS-PDSCH is two
slots delayed from the HS-SCCH, but this is because the mobile
station receives the modulation scheme information via HS-SCCH, and
then enables the demodulation of HS-PDSCH by a demodulation scheme
according to this modulation scheme. In HS-SCCH and HS-PDSCH, three
slots constitute one sub-frame.
The HS-DPCCH is a channel in an upstream direction, and the first
slot thereof is used to transmit an ACK/NACK signal to show the
receive result of HS-PDSCH from the mobile station to the radio
base station when about 7.5 slots elapse after the receipt of
HS-PDSCH. The second and third slots are used to feedback and
regularly transmit the CQI information for adaptive modulation
control to the base station. The CQI information to be transmitted
is calculated based on the receive environment (SIR measurement
result of CPICH) measured during the period of four slots before to
one slot before in the CQI transmission.
Handover
The mobile station 7 is communicating data via the HS-PDSCH with
the base station 61 of the serving cell (see (A) of FIG. 18). At
this time, handover status occurs if the mobile station 7
approaches an adjacent cell (non-serving cell) by moving (see (B)
of FIG. 18). And when the quality of signals received from the base
station 6.sub.2 of the non-serving cell, such as SIR (Signal to
Interference Ratio), becomes better than the SIR of the signals
received from the base station 6.sub.1 of the serving cell, the RNC
switches the communication base station from the base station
6.sub.1 to the base station 6.sub.2 (see (C) of FIG. 18), and
transmits data from the base station 6.sub.2 to the mobile station
7 via HS-PDSCH.
The downstream signal from each cell has a different scrambling
code, so each signal is demultiplexed by de-spreading using the
respective scrambling code at a mobile station. The receive signal
includes a common pilot signal CPICH, so the mobile station
de-spreads the receive signal by the scrambling code and
demultiplexies CPICH signal base station by base station.
Thereafter the CPICH signal is multiplied by the channelization
code for de-spreading, and by this the average power of CPICH
signal and the variance value thereof are derived, and SIR is
determined for each cell using the power of CPICH signal. And the
SIR of each cell is compared one another, and the cell having the
highest SIR is notified to the base station as a candidate of
handover destination.
FIG. 19 shows the sequence of handover, and in HSDPA, handover is
performed as a hard handover.
When the mobile station 7 is communicating with the base station
6.sub.1 in the serving cell (step S1), and when SIR, which is the
receive quality from the base station 6.sub.2 of the non-serving
cell, becomes good, the mobile station 7 notifies the SIR of the
signal received from each base station 6.sub.1 and 6.sub.2 to the
RNC 2 via the higher logical channel DCCH (step S2). When the SIR
report which is channel switching request is received, the RNC 2
instructs the base station 6.sub.2 to start up the communication
channel (HS-PDSCH) allocated to the communication between the
mobile station 7 and the base station 6.sub.2 Of the non-serving
cell (handover request, step S3). When the instruction to start up
the communication channel is received, the base station 6.sub.2
responds with a confirmation (step S4).
Then the RNC 2 notifies the communication channel (HS-PDSCH) of the
handover destination to the mobile station 7 via the base station
6.sub.1 during communication (step S5). When the information on the
communication channel of the handover destination is received, the
mobile station 7 immediately switches the channel according to the
communication channel, and enables communication with the base
station 6.sub.2, and hereafter transmits/receives synchronization
burst signals and communication burst signals to establish frame
synchronization and to adjust time alignment with the destination
base station 6.sub.2. And when normal communication becomes
possible, the base station 6.sub.2 of the serving cell reports the
channel start-up completion to the RNC 2 (handover: step S6). When
the channel start-up completion signal is received, the RNC 2 sends
an instruction to release the channel to the base station 6.sub.1,
and ends handover (step S7). Hereafter the mobile station 7
communicates data with the base station 6.sub.2 via HS-PDSCH. At
this time, HS-SCCH is also switched and a reception of data via
HS-PDSCH is attempted when data which is transmitted from the base
station 6.sub.2 via HS-SCCH is received.
Problems of Conventional Handover
To perform handover control, a mobile station measures the SIR
quality of the receive signals from the serving cell, which is
currently transmitting the HS-PDSCH signals, and the SIR quality of
the receive signals from other non-serving cells. To measure these
SIRs, power of CPICH signal, which is transmitted from each cell,
is used. The ratio of the CPICH power to the total receive power
from the serving cell, where HS-PDSCH signals are transmitted to
the mobile station, is smaller than the ratio to the total receive
power from the non-serving cells where HS-PDSCH signals are not
transmitted to the mobile station.
The mobile station, in which an analog circuit is used for the
receiver, generates fixed noise components by NF (Noise Figure) of
the receiver, waveform distortion due to a filter and local phase
noise. The CPICH signal of each cell is influenced by internal
noise in the receive step, and in the signals from the base station
transmitting data via HS-PDSCH, the SN ratio is small since the
ratio of CPICH power to the total receive power is small, and as a
result SIR is small.
As described above, SIR of the serving cells may decrease during
handover by the amount of the influence of the HS-PDSCH signal. On
the other hand, when another cell is not transmitting data via
HS-PDSCH or when the power thereof is small, the deterioration of
SIR could be small since the interference of HS-PDSCH is minimal.
As a result, handover to the other cell which is an non-serving
cell, is likely to occur easily. And if handover occurs here, the
transmission of the signals of HS-PDSCH shifts to the other cell as
a new serving cell. As a result, the data is transmitted from the
new serving cell to the mobile station via HS-PDSCH instead, and
interference increases and the SIR value of the new serving cell
tends to drop. In the old serving cell, on the other hand, the data
is not transmitted to the mobile station via HS-PDSCH after
handover has completed, therefore interference decreases, SIR
increases and SIR of the old serving cell may be higher than SIR of
the new serving cell. HS-PDSCH is a hard handover, so every time a
handover occurs the communication is interrupted and the throughput
drops.
The reason why the SIR of signals from the base station, which
transmits data through HS-PDSCH, decreases will be described. The
power of the signals received by the antenna is composed of CPICH
power, HS-PDSCH power, other channel power and external noise
power, as shown in FIG. 20. The total receive power is the total of
these powers, and as FIG. 21 shows, internal noise according to the
value of this total receive power is generated. The total receive
power is given by the following expression.
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times. ##EQU00001## The internal noise
power is a value corresponding to the total receive power, and is
given by the following expression,
Internal noise power [mW]=total receive power [mW]/.eta., and this
is converted to the following expression using by logarithm,
Internal noise power [dBm]=total receive power [dBm]-internal noise
power ratio [dB] (2) In addition, the total noise power can be
given by Total noise power [dBm]=10 log.sub.10{external noise
power[mW]+internal noise power [mW]} (3) and SIR, which is
calculated from CPICH, is in proportion to the ratio of the CPICH
power and the total noise power, as shown in FIG. 22, so SIR can be
calculated by the following formula. SIR [dB]=CPICH power
[dBm]-total noise power [dBm]+CPICH spreading gain [dB] (4) Here it
is assumed that the signals of HS-PDSCH have stopped, as shown in
FIG. 23. When HS-PDSCH power stops, the total receive power
decreases, as shown in FIG. 24, and according to this, the internal
noise power and the total noise power decrease. Since the CPICH
power does not change depending on whether HS-PDSCH power stops or
not, as a result SIR increases, as shown in FIG. 25.
As described above, SIR is measured to be low when data is being
received via HS-PDSCH, and SIR is measured to be high when data is
not being received via HS-PDSCH. In other words, the SIR of the
signal from a base station which is transmitting data via HS-PDSCH
decreases, and the SIR of the signal from a base station which is
not transmitting data via HS-PDSCH increases.
In this way, if a mobile station moves and a handover occurs during
HS service (during status of waiting for receipt of data via
HS-PDSCH), SIR tends to drop in a new serving cell and SIR tends to
increase in a old serving cell, and this influence is particularly
strong when high-speed transmission is performed at high power.
Because of this, the SIR measurement conditions differ between the
serving cell and non-serving cell, and handover tends to occur
sooner rather than at the correct timing.
In the case of HS-PDSCH, which uses a hard handover, the power of
the HS-PDSCH shifts to the next base station after handover
completes, so the SIR of the next base station is measured low
while the SIR of the previous base station is measured high, which
causes handover again.
SUMMARY OF THE INVENTION
With the foregoing in view, it is an object of the present
invention to control handover by measuring the communication
environment between each cell (serving cell and non-serving cell)
and a mobile station, such as the SIR of receive signals, under
conditions that are nearly identical.
It is another object of the present invention to prevent a drop in
communication throughput by controlling handover such that an
unnecessary handover is not generated.
It is still another object of the present invention to quickly
control the transmission rate according to the communication
environment by reporting a CQI value, based on the maximum SIR out
of the SIRs measured for handover control, to the base station of
the serving cells.
To solve the above problems, the present invention provides a
communication environment measurement method in a mobile station
included in a communication system which respectively transmits
pilot signals from a plurality of base stations to a mobile
station, and controls a hard handover by switching a channel for
data transmission to the mobile station based on the communication
environment between each base station and the mobile station,
including step of measuring the communication environment between a
source base station of the channel and the mobile station and the
communication environment between another base station and the
mobile station are measured for the handover control, and step of
compensating relative deterioration of the measurement result of
the communication environment on the source base station of the
channel in comparison with the measurement result of the
communication environment on the other base station, the relative
deterioration being caused by the transmission of the channel.
In the above method, the compensating step includes correcting
total receive power by subtracting power of a signal transmitted to
the mobile station by way of the channel from the total receive
power of signals transmitted from the source base station;
calculating total noise power based on the total receive power
after the correction; and measuring the communication environment
between the source base station of the channel and the mobile
station using power of the pilot signal received from the source
base station of the channel and the total noise power.
Alternatively in the above method, the compensating step includes
estimating signal power in a case where a signal is received from
the other base station via the channel, correcting total receive
power by adding the estimated signal power to the total receive
power of signals received from the other base station, calculating
the total noise power based on the total receive power after the
correction, and measuring the communication environment between the
other base station and the mobile station using power of the pilot
signal received from the other base station and the total noise
power.
To solve the above problems, the present invention provides a
mobile station included in a communication system which
respectively transmits pilot signals from a plurality of base
stations to a mobile station and controls a hard handover by
switching a channel for data transmission to the mobile station
based on the communication environment between each based station
and the mobile station, comprising a measuring unit for measuring
the communication environment between a source base station of the
channel and the mobile station and the communication environment
between another base station and the mobile station for hard
handover control, and a compensation unit for compensating relative
deterioration of the measurement result of the communication
environment on the source base station of the channel in comparison
with the measurement result of the communication environment on the
other base station, the relative deterioration being caused by the
transmission of the channel.
In the above mobile station, the compensation unit comprises: a
total receive power measurement unit for measuring total receive
power of the signals received from the source base station of the
channel; a signal power measurement unit for measuring power of the
signal of the channel received from the source base station of the
channel; a pilot signal power measurement unit for measuring signal
power of the pilot signals received from the source base station of
the channel; and a communication environment measurement unit for
correcting the total receive power by subtracting the power of the
signal received via the channel from the total receive power,
calculating total noise power based on the total receive power
after the correction, and measuring the communication environment
between the source base station of the channel and the mobile
station using the pilot signal power and the total noise power.
Alternatively the compensation unit further includes: a total
receive power measurement unit for measuring total receive power of
the signals received from the other base station; a pilot signal
power measurement unit for measuring signal power of the pilot
signal received from the other base station; and a communication
environment measurement unit for estimating signal power in a case
where a signal is received from the other base station via the
channel, correcting the total receive power by adding the estimated
signal power to the total receive power of the signals received
from the other base station, calculating total noise power based on
the total receive power after the correction, and measuring the
communication environment between the other station and the mobile
station using the signal power of the pilot signal received from
the other base station and the total noise power.
Further alternatively the compensation unit comprises: a judgment
unit for judging the timing when data is communicated via the
channel referring to the control channel to be transmitted from the
source base station of the channel; a communication environment
measurement unit for measuring the communication environment
between the source base station of the channel and the mobile
station based on the pilot signal received from the source base
station of the channel at the timing; and a communication
environment measurement unit for measuring the communication
environment between the other base station and the mobile station
based on the pilot signal received from the other base station
which is not in-communication.
The mobile station further comprises means for determining maximum
SIR, which is a ratio of the pilot signal power and the noise
signal power, out of the SIRs of a plurality of base stations
measured when the communication environment between the base
station and the mobile station was measured as SIR, and means for
feeding back the communication environment instruction value
corresponding to the maximum SIR to the source base station.
According to the present invention, the communication environment,
such as SIR, between the serving cells/non-serving cells and a
mobile station, can be measured under the same conditions, so the
quality of the communication environment can be accurately judged
and handover can be controlled based on this judgment, therefore
handover can be executed at a correct timing.
Also according to the present invention, the communication
environment, such as the SIR of receive signals, between the
serving cells/non-serving cells and a mobile station, can be
measured under the same conditions, so the quality of the
communication environment can be accurately judged and handover can
be controlled based on this judgment, therefore the generation of
unnecessary handover can be avoided and a drop in the communication
throughput can be prevented.
Also according to the present invention, a CQI value corresponding
to the maximum SIR out of the SIRs measured for handover control is
reported to the serving cell, so even if the serving cell is
switched by handover, the transmission rate can be quickly
controlled according to the communication environment of the
serving cell.
Other features and advantages of the present invention will be
apparent from the following description taken in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram depicting the mobile station of a first
embodiment;
FIG. 2 is a block diagram depicting the receiver;
FIG. 3 are diagrams depicting the SIR measurement method of the SIR
measurement unit;
FIG. 4 is a diagram depicting the handover status;
FIG. 5 is a flow chart depicting the handover control according to
the first embodiment;
FIG. 6 is a flow chart depicting the processing of the measuring
ratio of the internal noise power and the total receive power in
the receiver of the mobile station, and the creating and saving of
the table of the receive noise power ratio with respect to the
total receive power;
FIG. 7 is a graph depicting the characteristics of the receive
noise power ratio;
FIG. 8 is a flow chart depicting the measurement processing of the
receive quality SIR1 when data is not being received from the
serving cell via HS-PDSCH;
FIG. 9 is a block diagram depicting the de-spreading/quality
measurement unit for serving the cells and non-serving cells of a
second embodiment;
FIG. 10 is a flow chart depicting the handover control according to
the second embodiment;
FIG. 11 is a flow chart depicting the receive quality SIR2
measurement processing when data is being received from a
non-serving cell via HS-PDSCH;
FIG. 12 is a block diagram depicting the mobile station of a third
embodiment;
FIG. 13 is a flow chart depicting the handover control of the third
embodiment;
FIG. 14 is a diagram depicting a variant form;
FIG. 15 is a block diagram depicting the W-CDMA (UMTS) mobile
communication system;
FIG. 16 is a diagram depicting a main radio channel used for
HSDPA;
FIG. 17 is a diagram depicting the timing of the channel in the
HSDPA system;
FIG. 18 are diagrams depicting handover;
FIG. 19 is a diagram depicting the handover sequence;
FIG. 20 is a diagram depicting the power of signals received at the
antenna terminal;
FIG. 21 is a diagram depicting the internal noise according to the
total receive power;
FIG. 22 is a diagram depicting an SIR which is a ratio of the CPICH
power and the total noise power;
FIG. 23 is a diagram depicting the powers when the signal via
HS-PDSCH is not received;
FIG. 24 is a diagram depicting the internal noise power when the
power of HS-PDSCH is not used; and
FIG. 25 is a diagram depicting the SIR when the power of HS-PDSCH
is not used.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the case of a communication system for respectively transmitting
pilot signals from a plurality of base stations to a mobile station
via the first channel (e.g. CPICH), and transmitting data to the
mobile station from one of the base stations via the second channel
(e.g. HS-PDSCH) on which hard handover is executed, a base station
which communicates with a mobile station is switched based on the
communication environment, such as SIR, between each base station
and the mobile station, so that the mobile station is able to
continue communication while moving (handover). For this, the
mobile station measures the communication environment of a base
station which is in-communication via the second channel and that
of the adjacent base station which is not in-communication under
the same conditions, and notifies the result to the network
side.
When the communication environment between the mobile station and
the base station in-communication is measured, the mobile station
corrects the total receive power by subtracting the receive power
of the signal received via the second channel from the total
receive power of the signals received from the base station
in-communication, and corrects the total noise power based on this
total receive power after the correction, and measures the
communication environment between the base station in-communication
and the mobile station using the signal power of the pilot signals
received from the base station in-communication and the corrected
total noise power. By this, on the assumption that data is not
communicated via the second channel, the communication environment
of the base station in-communication can be estimated. As to
communication environment of a base station which is not
in-communication, on the other hand, the mobile station measures
the communication environment between this base station, which is
not in-communication, and the mobile station using the pilot
signals received from the base station which is not
in-communication. By this, the communication environment at the
time when each base station is not communicating data in the second
channel, can be measured and notified to the network side.
(A) First Embodiment
Configuration of Mobile Station
FIG. 1 is a block diagram depicting the mobile station of the
present invention. The signal transmitted from the base station is
input to the receiver 13 via the antenna 11 and the duplexer 12. As
FIG. 2 shows, the receiver 13 comprises the high frequency
amplifier 51, band pass filter 52 for limiting the band, frequency
conversion unit 53 for converting RF signals into base band signals
in frequency, low pass filter 54 for limiting the high band, gain
variable amplifier 55 and AD converter 56 for converting input
signals into analog signals.
The base station demultiplexing unit 14 multiplies the receiver
output signal by the scrambling code of the serving cell or the
adjacent non-serving cell (de-spreading) when necessary,
demultiplexes the signals from a base station of each cell; and
outputs them. The AGC control unit 15 determines the gain control
value of the gain variable amplifier 55 (FIG. 2), so that the
signal level to be received from the base station becomes the set
level, and inputs the gain control value to the gain variable
amplifier 55 via the DA converter 16. The gain control value of the
AGC control unit 15 corresponds to the total receive power from the
base station. Therefore the total receive power measurement unit 17
has a conversion table between the gain control value and the total
receive power, and determines the total receive power from this
table based on the AGC control value which is input from the AGC
control unit 15, and outputs it.
The path search unit 18 multiplies the signal received from the
base station of the serving cell by the spreading code
(channelization code), detects the multi-path, and inputs the path
timing to the HS-PDSCH de-spreading unit 19 and the CPICH
de-spreading unit 20 of the de-spreading/quality measurement unit
10.sub.1, for serving cells. The HS-PDSCH de-spreading unit 19
de-spreads at each path timing of the multi-path which was input,
and the channel estimation/compensation unit 21 estimates a channel
and performs channel compensation on the HS-PDSCH de-spreading
signal based on this channel estimation value. The rake combiner 22
combines the de-spreading signal to be output at each path timing
where channel compensation was performed, and the decoding unit 23
demodulates and decodes the rake combination signal, and the error
detection unit 24 detects errors by the CRC operation, and outputs
the CRC result. The ACK/NACK generation unit 25 generates the
ACK/NACK signal based on the CRC check result. In the receive noise
power ratio table 26 of a storage unit, the receive noise power
ratio which is a ratio of the internal noise power and the total
receive power of the receiver, is measured and set in advance.
The HS-PDSCH power measurement unit 31 in the receive quality
measurement unit 30, which is a communication environment
measurement unit, measures the HS-PDSCH power using the output
signal of the HS-PDSCH de-spreading unit 19, and inputs it to the
SIR correction unit 32, the SIR measurement unit 33 measures SIR at
the time when data is received via HS-PDSCH, and inputs it to the
SIR correction unit 32, and the CPICH power measurement unit 34
measures the CPICH power using the output signal of the CPICH
de-spreading unit 20, and inputs it to the SIR correction unit 32.
The SIR correction unit 32 executes correction control of the SIR
using the total receive power, HS-PDSCH power, SIR, CPICH power and
receive noise power ratio, and inputs the corrected SIR (=SIR1)
after correction to the SIR report unit 41 and also to the CQI
conversion unit 42. The correction control of the SIR is detailed
hereinafter.
The receive quality measurement unit 30 has a configuration for
measuring and cottecting the SIR of serving cells, but the receive
quality measurement unit 30 (not shown in FIG. 1) installed in the
de-spreading/quality measurement unit 10.sub.2 for non-serving
cells requires only the SIR measurement unit 33, and this SIR
measurement unit 33 measures SIR in accordance with a method later
mentioned, and inputs it to the SIR reporting unit 41 as SIR2.
The SIR reporting unit 41 transmits the measured SIR1 and SIR2 to
the RNC (Radio Network Controller) via the logical channel DCCH
(Dedicated Control Channel), which is a higher layer. The CQI
conversion unit 42 converts the SIR1 into a CQI value which
regulates the block error rate BLER not to exceed 0.1, and the
HS-DPCCH mapping unit 43 maps the CQI value and the ACK/NACK in the
sub-frame of the HS-DPCCH, and sends it to the base station. The
DPCH mapping unit 44 maps the individual data in the dedicated
physical channel (DPCH), and sends it to the base station.
The synthesis unit 45 synthesizes the DCCH signal, HS-DPCCH signal
and DPCH signal, the synthesized signal is spread by the scrambling
code in the spreading unit 46, and is input to the transmitter 49
via the FIR filter 47 and DA converter 48. The transmitter 49
converts the base band signal into a high frequency signal, and
transmits it to the base station via the duplexer 12 and antenna
11.
Measurement of SIR
FIG. 3 describes the SIR measurement method of the SIR measurement
unit 33. The constellation of the CPICH exists at a predetermined
position of the I-Q complex plane at the transmission side, as
shown in (A) of FIG. 3. The constellation of the CPICH scatters at
the receive side, as shown in (B) of FIG. 3, influenced by noise.
The average value of the receive CPICH is the signal component S
where the dispersion from the average is the interference component
I, and the ratio of the signal component S and the interference
component I is SIR.
When the de-spreading signal at the m-th path, with respect to the
n-th pilot symbol at the k-th slot is expressed by r.sub.m (n, k),
the average thereof of the Np symbols is given by the following
expression.
.function..times..times..times..function. ##EQU00002## Here m is
1.ltoreq.m.ltoreq.M (M is a number of paths of the multi-path).
Also the average power of the pilot signals is given by the
following expression. {tilde over (S)}.sub.m(k)=| r.sub.m(k)|.sup.2
The power (interference power) of the difference between the
average of the pilot signals and each pilot signal is given by the
following expression.
.function..times..times..function..function. ##EQU00003## To
improve accuracy, the slot average of the interference power is
determined by the following expression, .sub.m(k)=.mu.
.sub.m(k-1)+(1-.mu.) .sub.m(k) and the average of the ratio of the
respective S and I of all the paths is calculated by the following
expression,
.function..times..times..times..times..times..function..function.
##EQU00004## then the SIR of the k-th slot is determined.
SIR Measurement Control in Serving Cells
As FIG. 4 shows, when the mobile station MS enters the boundary
area between the serving cell SCL and the non-serving cell NSCL,
the handover status is generated, where the SIR of the signal
received from the base stations BS1 and BS2 of each cell is
measured, and is sent to the RNC (Radio Network Controller).
FIG. 5 is a flow chart depicting the handover control of the first
embodiment. In the handover status, the mobile station MS measures
the receive quality SIR1 on the assumption that data is not
received from the serving cell SCL via HS-PDSCH (step 101). Then
the mobile station MS measures the receive quality SIR2 for the
non-serving cell NSCL (step 102), and reports SIR1 and SIR2 to the
RNC device respectively via the logical channel DCCH (step 103).
The RNC compares the values of SIR1 and SIR2 (step 104), and sends
a handover request to the base station BS2 of the non-serving cell
(NSCL) if SIR1<SIR2, and executes handover hereafter according
to the sequence shown in FIG. 19 (step 105).
When the receive quality SIR1 in the serving cell SCL is measured,
the ratio of the internal noise power and the total receive power
of the receiver of the mobile station is measured in advance
according to FIG. 6, and the ratio of the internal noise power to
the total receive power is created and stored in the receive noise
power ratio table 26 of the storage unit (FIG. 1) (step 201). FIG.
7 is a graph depicting the characteristics of the receive noise
power ratio, which corresponds to Expression (2). This is required
to measure the receive quality SIR1 on the assumption that the data
is not received via HS-PDSCH.
FIG. 8 is a flow chart depicting the receive quality SIR1
measurement processing on the assumption that data is not being
received via HS-PDSCH for the serving cell SCL. First the total
noise power N.sub.T (dBm), when data is being received via
HS-PDSCH, is calculated by the following expression, which is
expression (4) modified, that is Total noise power N.sub.T
[dBm]=CPICH power [dBm]-SIR [dB]+CPICH spreading gain [dB] (4)'
(step 301). The CPICH power and SIR can be measured by the mobile
station, and the CPICH spreading gain is a known value, so N.sub.T
[dBm] can be derived from these values.
Now the internal noise power is calculated by expression (2), when
data is being received via HS-PDSCH, that is Internal noise power
[dBm]=total receive power [dBm]-internal noise power ratio [dB] (2)
(step 302). This expression can be calculated by finding the
internal noise power ratio [dB] from the receive noise power ratio
table 26, which is measured and stored in advance in step 201.
Then the external noise power is calculated from the total noise
power N.sub.T [dBm] and the internal noise power using the
following expression, that is External noise power
[mW]=10.sup.(NT[dBm]/1O)-internal noise power [mW] (5) (step 303).
This external noise power is constant without depending on whether
data is received via HS-PDSCH or not, this means that the external
noise power when data is not being received via HS-PDSCH is
determined here.
After calculation of the external noise power ends, the internal
noise power when data is not being received via HS-PDSCH is
calculated. First the total receive power PT' [dBm] is calculated
by the following expression Total receive power PT' [dBm]=10
log.sub.10 {total receive power [mW]-HS-PDSCH power [mW]} (6) (step
304). Then the internal noise power ratio [dB] corresponding to the
total receive power PT' [dBm], is determined from the receive noise
power ratio table 26, and the internal noise power when data is not
being received via HS-PDSCH is calculated by expression (2) (step
305).
If the internal noise power and external noise power when data is
not being received via HS-PDSCH are determined, then the total
noise power [dBm] when data is not being received via HS-PDSCH is
calculated by the following expression. Total noise power [dBm]=10
log.sub.10 {external noise power[mW]+internal noise power[mW]} (7)
(step 306), and from this result, SIR1, when data is not being
received via HS-PDSCH, is calculated by the following expression
SIR1 [dB]=CPICH power [dBm]-total noise power [dBm]+CPICH spreading
gain [dB] (8) This SIR1 is used for handover control.
According to the first embodiment, the SIR of the receive signals
from a serving cell is measured, on the assumption that data is not
being received via HS-PDSCH. As a result, the SIR measurement
condition for the serving cell can be same as the SIR measurement
condition of the non-serving cell, and SIRs can be correctly
compared, so unnecessary handover can be avoided and a drop in the
communication throughput can be prevented.
(B) Second Embodiment
In the first embodiment, SIR is estimated in a serving cell on
assumption that data is not being received via HS-PDSCH, so that
SIR can be measured and compared under the identical conditions for
a serving cell and non-serving cell. In the second embodiment, SIR
is estimated on assumption that data is being received from a
non-serving cell via HS-PDSCH, so that SIR can be measured and
compared under the identical conditions for a serving cell and
non-serving cell.
FIG. 9 is a block diagram depicting the de-spreading/quality
measurement units 10.sub.1 and 10.sub.2 of the serving cell and
non-serving cell according to the second embodiment, where the
elements that are same as the elements in the despreading/quality
measurement unit in FIG. 1 are denoted with the same reference
numerals. The differences are:
(1) the SIR correction unit 32 is removed from the
de-spreading/quality measurement unit 10.sub.1 of the serving cell,
and SIR measured by the SIR measurement unit 33 is output as
SIR1;
(2) HS-PDSCH power and CPICH power are input to the SIR correction
unit 32 of the de-spreading/quality measurement unit 10.sub.2 of
the non-serving cell;
(3) the HS-PDSCH de-spreading unit 19 and the HS-PDSCH power
measurement unit 31 are removed from the de-spreading/quality
measurement unit 10.sub.2 of the non-serving cell; and
(4) the SIR correction unit 32 of the de-spreading/quality
measurement unit 10.sub.2 of the non-serving cell estimates and
outputs SIR when data is being received via HS-PDSCH from the
non-serving cell.
FIG. 10 is a flow chart depicting the handover control according to
the second embodiment. In handover status, the mobile station
measures the receive quality SIR1 for the serving cell SCL (FIG. 4)
(step 401). Then the mobile station measures the receive quality
SIR2 on assumption that data is being received from the non-serving
cell NSCL via HS-PDSCH (step 402), and reports each SIR1 and SIR2
to the RNC device via the logical channel DCCH (step 403). RNC
compares the values of SIR1 and SIR2 (step 404), and sends the
handover request to the base station BS2 of the non-serving cell
NSCL if SIR1<SIR2, and then performs handover according to the
sequence shown in FIG. 19 (step 405).
FIG. 11 is a flow chart depicting the receive quality SIR2
measurement processing on assumption that data is being received
via HS-PDSCH from the non-serving cell NSCL (FIG. 4).
The SIR correction unit 32 determines the ratio .phi. of the
HS-PDSCH power and the CPICH power of the serving cell to be input
from the de-spreading/quality measurement unit 10.sub.1 of the
serving cell, and stores it (step 501). Then the SIR correction
unit 32 determines the internal noise power and the external noise
power in the non-serving cell by Expressions (2) and (5) (step
502).
After the internal noise power and the external noise power are
determined, the CPICH power P.sub.CPICH [mW] in the non-serving
cell is determined, and .phi..times.P.sub.CPICH [mW] is estimated
as the HS-PDSCH power on assumption that data is being received via
HS-PDSCH in the non-serving cell (step 503). Then the total receive
power is calculated by the following expression, that is Total
receive power [dBm]=10 log.sub.10 {total receive power
[mW]+.phi..times.P.sub.CPICH [mW]} (9) (step 504). Then the
internal noise power is determined using the receive noise power
ratio table 26 (step 505), and the total noise power [dBm] is
calculated by the following expression Total noise power [dBm]=10
log.sub.10 {external noise power[mW]+internal noise power [mW]}(10)
(step 506). Finally SIR2 is calculated by the following expression
on the assumption that data is being received from the non-serving
cell via HS-PDSCH that is, SIR2 [dB]=CPICH power [dBm]-total noise
power [dBm]+CPICH spreading gain [dB] (11) (step 507), and this
SIR2 is used for handover control.
According to the second embodiment, SIR of the receive signal from
a non-serving cell is measured on the assumption that data is
received from this non-serving cell via HS-PDSCH and compared with
the SIR of the receive signal from the serving cell to control
handover, therefore the condition of SIR measurement for the
serving cell can be same as the condition of SIR measurement for
the non-serving cell, and SIRs can be correctly compared, so
unnecessary handover can be avoided and a drop in the communication
throughput can be prevented.
(3) Third Embodiment
In the third embodiment, a mobile station demodulates HS-SCCH
detects a slot which data is not being transmitted via HS-PDSCH,
measures the SIR in the slot, and uses this SIR for handover,
thereby the SIR measurement condition for the serving cell can be
same as the condition of SIR measurement for the non-serving
cell.
FIG. 12 is a block diagram of the third embodiment depicting the
mobile station where elements that are same as the elements of the
first embodiment in FIG. 1 are denoted with the same reference
numerals. The differences are that an HS-SCCH measurement unit 40
is installed, and that the SIR measurement unit 33 measures the SIR
in a slot where data is not being transmitted via HS-PDSCH, and
outputs it as SIR1.
FIG. 13 is a flow chart depicting the handover control of the third
embodiment. When the handover status is generated, the mobile
station demodulates the data received from the serving cell SCL via
HS-SCCH, and identifies a slot which is not transmitting data via
HS-PDSCH referring to the demodulated control information (step
601). Then the SIR of the receive signal at the above mentioned
slot timing in the serving cell SCL is measured as SIR1 (step 602).
Then the mobile station measures the receive quality SIR2 for the
non-serving cell NSCL (step 603), and each SIR1 and SIR2 are
reported to the RNC device via the logical channel DCCH (step 604).
The RNC compares the values of SIR1 and SIR2 (step 605), transmits
the handover request to the base station BS2 of the non-serving
cell NSCL if SIR1<SIR2, and then handover is executed according
to the sequence shown in FIG. 19 (step 606).
According to the third embodiment, SIR can be measured when data is
not being received from the serving cell via HS-PDSCH, and SIR
measurement conditions can be the same for the serving cell and the
non-serving cell, therefore SIRs can be compared at high
precision.
Variant Form
The first to third embodiments can be configured such that SIR is
determined under the same SIR measurement conditions, and a CQI
value, corresponding to the maximum SIR among the determined SIRs,
is determined and reported to the base station. In other words, as
FIG. 14 shows, SIR1 and SIR2, which are output from the
de-spreading/quality measurement units 10.sub.1 and 10.sub.2 of the
serving cell and the non-serving cell, are input to the CQI
conversion unit 42. The CQI conversion unit 42 determines the CQI
according to the maximum SIR and reports it to the base
station.
According to this variant form, a CQI value after handover is
reported to the base station quicker and the transmission rate can
be controlled according to this CQI.
In the above description, the case when the present invention is
applied to an HSDPA system was described, but the present invention
can be applied to other similar communication systems. The present
invention was described for the case when the communication
environment between the base station and the mobile station is
measured using SIR, but the present invention is not limited to
using an SIR.
As many apparently widely different embodiments of the present
invention can be made without departing from the spirit and scope
thereof, it is to be understood that the invention is not limited
to the specific embodiments thereof except as defined by the
appended Claims.
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